Backs up, having lost a kilo with dried, crusty skin (4)
I believe the answer is:
scab
'skin' is the definition.
The answer and definition can be both body parts as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for scab that I've seen before include "Rat" , "Ignorer of strike" , "Crust on wound, or a blackleg" , "He's not out" , "that blocks cut" .)